1. Field of the Invention
The present invention relates to a display device, and more particularly to the enhancement of a display quality in a display device which performs a display control of a pixel using a thin film transistor (hereinafter simply referred to as “TFT”).
2. Description of the Related Art
In a display device such as a liquid crystal display device, a display control of each pixel is performed using a TFT or the like. With respect to the TFT, there has been generally known the bottom gate structure where a gate electrode is positioned closer to a light source than a semiconductor film. In radiating light to the TFT having such structure from a light source such as a backlight, the gate electrode per se functions as a light blocking mask for a semiconductor film which faces the gate electrode in an opposed manner.
When light is radiated to the semiconductor film, hole electron pairs are generated, and the degree of generation of the hole electron pairs is, particularly in case of a TFT which uses polycrystalline silicon, remarkably lowered along with the increase of the concentration of a carrier. Accordingly, in a channel region, or a depletion layer region which is formed in a PN junction portion in the vicinity of the channel region, hole electron pairs are liable to be easily generated compared to a source region or a drain region doped with high concentration of an impurity which constitutes a carrier. Unless these regions are sufficiently shielded from light by the gate electrode which faces these regions in an opposed manner, hole electron pairs are generated so that a light leakage current is generated thus increasing an OFF current. Hereinafter, the source region, the drain region and the like are collectively referred to as a high concentration region.
Further, as the structure which suppresses a leak current, the LDD (Lightly Doped Drain) structure has been generally known. The LDD structure is configured such that between a channel region and a high concentration region, a region which is doped with low concentration of an impurity compared to the high concentration region (hereinafter referred to as “low concentration region”) is formed.
As the related art which discloses such techniques, JP 2000-236097 A (patent document 1) and JP 2009-206434 A (patent document 2) are named.